/****************************************************************************
 * net/bluetooth/iob/iob_trimtail.c
 *
 *   Copyright (C) 2014, 2017 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <tinyara/config.h>

#include <string.h>
#include <debug.h>

#include <tinyara/bluetooth/iob/iob.h>

#include "iob.h"

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: iob_trimtail
 *
 * Description:
 *   Remove bytes from the end of an I/O chain
 *
 ****************************************************************************/

FAR struct iob_s *iob_trimtail(FAR struct iob_s *iob, unsigned int trimlen)
{
	FAR struct iob_s *entry;
	FAR struct iob_s *penultimate;
	FAR struct iob_s *last;
	int len;

	iobinfo("iob=%p pktlen=%d trimlen=%d\n", iob, iob->io_pktlen, trimlen);

	if (iob && trimlen > 0) {
		len = trimlen;

		/* Loop until complete the trim */

		while (len > 0) {
			/* Calculate the total length of the data in the I/O buffer
			 * chain and find the last entry in the chain.
			 */

			penultimate = NULL;
			last = NULL;

			for (entry = iob; entry; entry = entry->io_flink) {
				/* Remember the last and the next to the last in the chain */

				penultimate = last;
				last = entry;
			}

			/* Trim from the last entry in the chain.  Do we trim this entire
			 * I/O buffer away?
			 */

			iobinfo("iob=%p len=%d vs %d\n", last, last->io_len, len);
			if (last->io_len <= len) {
				/* Yes.. Consume the entire buffer */

				iob->io_pktlen -= last->io_len;
				len -= last->io_len;
				last->io_len = 0;

				/* Free the last, empty buffer in the list */

				iob_free(last);

				/* There should be a buffer before this one */

				if (!penultimate) {
					/* No.. we just freed the head of the chain */

					return NULL;
				}

				/* Unlink the penultimate from the freed buffer */

				penultimate->io_flink = NULL;
			}

			else {
				/* No, then just take what we need from this I/O buffer and
				 * stop the trim.
				 */

				iob->io_pktlen -= len;
				last->io_len -= len;
				len = 0;
			}
		}
	}

	return iob;
}
